Experimental and Clinical Psychopharmacology - Vol 24, Iss 6

Experimental and Clinical Psychopharmacology seeks to promote the discipline of psychopharmacology in its fullest diversity. Psychopharmacology necessarily involves behavioral change, psychological processes, or their physiological substrates as one central variable and psychopharmacological agents as a second central variable. Such agents will include drugs, medications, and chemicals encountered in the workplace or environment.
Copyright 2016 American Psychological Association

Directed forgetting of memories in cocaine users.Memory retrieval requires an effective recruitment of inhibitory control to successfully reject unnecessary memories. The use of cocaine is associated with poor cognitive control processes, but little is known about the impact of chronic and recreational use of cocaine on inhibitory control during intentional forgetting. We studied whether chronic and recreational users of cocaine show impairments on the mechanism responsible for intentional forgetting of memories. Two experiments were carried out on chronic cocaine users in rehabilitation (Experiment 1) and recreational cocaine polydrug users (Experiment 2) performing a directed forgetting (DF) task, an index of memory suppression. Participants were matched for sex, age, and intelligence (Raven’s standard progressive matrices) with cocaine-free controls and compared on their performance on a DF procedure. Chronic cocaine users in rehabilitation and recreational cocaine polydrug users, as compared with controls, were not able to intentionally suppress the required information and they did not show a reliable DF effect. The consumption of cocaine appears to alter the control processes implicated in intentional suppression of nonrelevant memories in episodic memory. The use of cocaine, even for recreational purposes, seems to be associated with poor performance in effectively triggering this control mechanism. The inability to suppress interference in declarative memory may have repercussion for daily activities. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

Individual differences in the reinforcing and subjective effects of d-amphetamine: Dimensions of impulsivity.Previous research has shown a relationship between impulsive personality and the subjective and reinforcing effects of d-amphetamine. Impulsive personality, however, is comprised of multiple dimensions. The association between different dimensions of impulsive personality and the subjective and reinforcing effects of d-amphetamine is unknown. The objective of this study was to assess the independent contributions of the “sensation-seeking” and “impulsivity” dimensions of the impulsive sensation-seeking subscale of the Zuckerman-Kuhlman Personality Questionnaire (ZKPQ) to the subjective and reinforcing effects of d-amphetamine. Forty healthy emerging adults varying in scores on the sensation-seeking and impulsivity dimensions of the ZKPQ participated in a double-blind, placebo-controlled, randomized study comprised of 4 2-day blocks. Each 2-day block consisted of a sample day and self-administration day. Subjective effects and physiological measurements were taken prior to, and hourly for 3 hr following, dose administration. On sample days participants were given 8 capsules containing 0, 1, or 2 mg d-amphetamine. On self-administration days participants were able to earn capsules containing the same dose of d-amphetamine that was administered on the previous sample day by responding on a Modified Progressive Ratio Task. The “sensation-seeking” dimension was positively associated with drug taking on the Modified Progressive Ratio Task, subjective effects (e.g., “good effect”), and heart rate. However, no clear relationship between the “impulsivity” dimension and outcome measures was observed. In conclusion, these data suggest that the narrow sensation-seeking dimension of impulsive sensation-seeking is associated with initial drug liking and drug taking behavior and may be a key predictor of drug use initiation. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

Comparing exponential and exponentiated models of drug demand in cocaine users.Drug purchase tasks provide rapid and efficient measurement of drug demand. Zero values (i.e., prices with zero consumption) present a quantitative challenge when using exponential demand models that exponentiated models may resolve. We aimed to replicate and advance the utility of using an exponentiated model by demonstrating construct validity (i.e., association with real-world drug use) and generalizability across drug commodities. Participants (N = 40 cocaine-using adults) completed Cocaine, Alcohol, and Cigarette Purchase Tasks evaluating hypothetical consumption across changes in price. Exponentiated and exponential models were fit to these data using different treatments of zero consumption values, including retaining zeros or replacing them with 0.1, 0.01, or 0.001. Excellent model fits were observed with the exponentiated model. Means and precision fluctuated with different replacement values when using the exponential model but were consistent for the exponentiated model. The exponentiated model provided the strongest correlation between derived demand intensity (Q0) and self-reported free consumption in all instances (Cocaine r = .88; Alcohol r = .97; Cigarette r = .91). Cocaine demand elasticity was positively correlated with alcohol and cigarette elasticity. Exponentiated parameters were associated with real-world drug use (e.g., weekly cocaine use) whereas these correlations were less consistent for exponential parameters. Our findings show that selection of zero replacement values affects demand parameters and their association with drug-use outcomes when using the exponential model but not the exponentiated model. This work supports the adoption of the exponentiated demand model by replicating improved fit and consistency and demonstrating construct validity and generalizability. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

Shallow discounting of delayed cocaine by male rhesus monkeys when immediate food is the choice alternative.Huskinson et al. (2015) recently examined delay discounting in monkeys choosing between an immediate drug (cocaine) reinforcer and a delayed nondrug (food) reinforcer. The present experiment examined the reverse situation: choice between immediate nondrug (food) and delayed drug (cocaine) reinforcers. Whereas the former choice situation exemplifies drug abuse from a delay-discounting perspective, our interest in the latter choice situation is derived from the observation that drug abusers, who characteristically are associated with impulsive choice, typically must devote considerable time to procuring drugs, often at the expense of immediate nondrug alternatives. Accordingly, we analyzed 3 male rhesus monkeys’ choices between immediate food and delayed cocaine (0.1 and 0.2 mg/kg/injection) using a hyperbolic model that allowed us to compare discounting rates between qualitatively different reinforcers. Choice of immediate food increased with food amount, and choice functions generally shifted leftward as delay to cocaine increased, indicating a decrease in the subjective value of cocaine. Compared with our previous delay-discounting experiment with immediate cocaine versus delayed food, both doses of delayed cocaine were discounted at a shallow rate. The present results demonstrate that rhesus monkeys will tolerate relatively long delays in an immediate-food versus delayed-drug situation, suggesting that in intertemporal choices between cocaine and food, the subjective value of cocaine is less affected by the delay until reinforcement than is the subjective value of delayed food. More generally, the present findings suggest that although drug abusers may choose impulsively when immediate drug reinforcement is available, they exercise self-control in the acquisition of a highly preferred, delayed drug reinforcer. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

Effects of methylphenidate on sensitivity to reinforcement delay and to reinforcement amount in pigeons: Implications for impulsive choice.Methylphenidate has been shown to decrease impulsive choice (increase choices of a larger more delayed reinforcer). The purpose of this study was to investigate 2 potential behavioral mechanisms of this effect: a drug-induced change in control by reinforcement delay (Experiment 1) and/or by reinforcement amount (Experiment 2). In Experiment 1, pigeons responded under a rapid-acquisition, concurrent-chains choice procedure involving delay to reinforcement; the option with the shorter delay varied unpredictably across sessions. The pigeons accurately tracked the shorter delay across sessions (i.e., a preference for the option with the shorter delay developed within each session). Methylphenidate selectively decreased sensitivity to reinforcement delay—it attenuated the acquisition of preference at doses that did not systematically affect bias or response rates. In Experiment 2, pigeons responded under a rapid-acquisition, concurrent-chains choice procedure involving reinforcement amount. The pigeons accurately tracked the option with the larger reinforcement amount across sessions. Methylphenidate selectively decreased sensitivity to reinforcement amount—it attenuated the acquisition of preference at doses that did not systematically affect bias or response rates. These data suggest that methylphenidate attenuates the degree to which the various reinforcement dimensions control choice, and that drug effects on impulsive choice depend upon the relative contributions of drug-induced changes in control of behavior by each relevant dimension. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

High-fat diet meal patterns during and after continuous nicotine treatment in male rats.Smoking to control body weight is an obstacle to smoking cessation, particularly in western cultures where diets are often rich in calories derived from fat sources. The purpose of this study was to investigate the effects of continuous nicotine administration on meal patterns in rats fed a high-fat diet. Male rats were housed in cages designed to continuously monitor food intake and implanted with minipumps to deliver approximately 1.00 mg/kg/day of nicotine or saline. Meal patterns and body weights were assessed for 2 weeks of treatment and 1 week posttreatment. When compared with controls, rats with continuous nicotine treatment exhibited a decrease in the average meal duration(s) during the first week of treatment and a modest, yet sustained reduction in daily number of meals over the 14-day treatment period. Nicotine-induced decreases in body weight gain were observed throughout the 2 weeks of treatment. No differences in meal patterns or body weight gain were seen for 1 week following cessation of treatment. Results from this study suggest that while continuous nicotine treatment decreases daily food intake, meal durations, meal numbers, and weight gain, cessation of this treatment does not result in significant compensatory increases. Understanding the effects of nicotine on feeding patterns and weight gain may allow for improvements in treatment protocols aimed at addressing the factors that contribute to tobacco use. (PsycINFO Database Record (c) 2016 APA, all rights reserved)

Effects of paclitaxel on mechanical sensitivity and morphine reward in male and female C57Bl6 mice.This study evaluated the hypothesis that a paclitaxel treatment regimen sufficient to produce mechanical allodynia would alter sensitivities of male and female mice to the conditioned rewarding and reinforcing effects of morphine. Saline or paclitaxel were administered on Days 1, 3, 5, and 7 in male and female C57Bl/6 mice to induce morphine-reversible mechanical allodynia as measured by the Von Frey filament test. Paclitaxel treatment did not change sensitivity to morphine conditioned place preference (CPP) relative to saline treatment in either male or female mice. Morphine produced peak self-administration under a fixed ratio-1 (FR1) schedule of reinforcement for 0.03 mg/kg morphine per infusion in female mice and 0.1 mg/kg morphine per infusion in male mice. During the progressive ratio experiments, saline treatment in male mice decreased the number of morphine infusions for 12 days whereas the paclitaxel-treated male mice maintained responding for morphine similar to baseline levels during the same time period. However, paclitaxel did not have an overall effect on the reinforcing efficacy of morphine assessed over a limited dose range during the course of the repeated self-administration. These results suggest that the reward-related behavioral effects of morphine are overall not robustly altered by the presence of paclitaxel treatment under the current dosing regimen, with the exception of maintaining a small yet significant higher baseline than saline treatment during the development of allodynia in male mice. (PsycINFO Database Record (c) 2016 APA, all rights reserved)